1. Field of the Invention
The present invention relates to an optical image measuring apparatus and a method of optically measuring an image, and particularly to, an image measuring apparatus for enhancing an accuracy of an image captured by an optical system and a method thereof.
2. Description of the Related Art
Electronic and mechanical components are vigorously being required to be made smaller and more accurate, and in order to check processing and manufacturing statuses of the small electronic and mechanical components, their sizes, shapes, and surface illuminance must be measured very precisely.
For example, sizes, shapes, laser marked statuses, and surface illuminance of an electronic component, that is, a semiconductor wafer and a micro-pattern of an integrated circuit fabricated on the semiconductor wafer cannot be measured by a conventional contact-type measuring apparatus. Moreover, in a case of using a contact-type surface illuminance measuring apparatus using a contact probe, a tip of the contact probe generates fine scratches on a surface of an object to be measured and it is hard to acquire information about an area thereof.
In order to solve the above problems, a 2-dimensional measuring apparatus and a method thereof and a 3-dimensional measuring apparatus and a method thereof, that use an optical microscope, have been developed to measure the shape of the object to be measured by projecting light emitted from a light source to the object to be measured according to a reference pattern and comparing the reference pattern with light modified due to the shape of the object.
There is proposed a method using white-light scanning interferometry (hereinafter, referred to as “WSI”) as the three-dimensional image measuring method using the micro-scope.
Generally, interference means a phenomenon that brightness is increased or decreased when two light beams are overlapped, and the WSI is a method of driving a micro-actuator, for example, a piezoelectric actuator to acquire an image while traveling on a reference plane so as to find an area where an interference pattern exists and after that to acquire a surface illuminance by finding a position where a visibility is maximal so that the three-dimensional image is measured.
FIG. 5 is a block diagram illustrating a process of acquiring an image in a conventional optical shape measuring apparatus.
The conventional shape measuring apparatus include a CCD camera 100 to take an image of an object and to output the image when a trigger signal is inputted from an image capturing device 205 that is described later, a plurality of lamps 400 installed at different places to adjust surface illuminance of parts of the object to be tested, and an illuminating controller 300 to control the plural lamps 400. The illuminating controller 300 controls the lamps 400 according to the trigger signal generated by the image capturing device 205 that is installed in a computer 200.
Meanwhile, the image capturing device 205 installed in the computer 200 performs a function of capturing the image outputted from the CCD camera 100 and transmitting the image to an image signal processor 207. The image capturing device 205 generates and outputs a trigger signal to synchronize the illuminating controller 300 and the CCD camera 100 and captures the image outputted from the CCD camera 100.
In this way, a plurality of heights in a scanning area of the object P is acquired to measure unevenness of the object P.
That the lamps are turned on by the trigger signal and an image of the object must be taken at this time is because the captured image must acquired while turning on the lamps 400 for acquiring an image of a surface of the object to be measured.
For reference, image signal processor 207 receives the captured image and processes and outputs the captured image into an image signal to be displayed on a display 209, and a controller 203 the processed image signal to the image capturing device 205 when an image measuring start command is inputted from a data input device 201.
In the conventional optical shape measuring system having the configuration as described above, only a starting point and an ending point of driving the piezoelectric actuator are determined using a piezoelectric controller, after that, the piezoelectric actuator is driven at constant speed, the CCD camera captures and outputs images whenever the image capturing unit generates trigger signals, and the image capturing unit at the rear side thereof captures and transmits the images outputted from the CCD camera and generates the trigger signal again thereafter. Therefore, it takes a long time for acquiring an image frame.
Moreover, since the piezoelectric actuator controller and the camera for capturing an image are driven at constant speed, a driving error may occur according to the shape of the object P.